FR2863582A1 - Sports board manufacturing procedure uses foam core blank thermoformed and compressed before covering with outer skin - Google Patents

Abstract

The procedure consists of making a blank for a rigid or thermoplastic foam core (24) which is thermoformed and compressed to create zones with different densities before covering with an outer skin (26). The thermoforming/compression stage produces zones with densities that differ by at least 20 per cent from the original blank, with the peripheral zone having a greater density, especially in the foot support area.

Description

METHOD FOR MANUFACTURING A SLIDING BOARD

  AND BOARD OBTAINED BY SUCH A METHOD

  The invention relates to the field of manufacturing methods of boards for gliding, including kitesurfing boards, surfing, and sailboards.

  The invention will here be more particularly described in the context of its application to a kitesurf board, that is to say a board for carrying the user on the water when it is towed by a kite. The kitesurf boards have for example dimensions of the order of 120 to 170 cm in length, for widths of the order of 30 to 60 cm, but they measure only a few centimeters of thickness.

  A common method for making such a board type is derived from the traditional construction of surfboards. A foam roll, manufactured by molding, is machined (by hand or with a numerically controlled machine) to obtain the shapes of the final core, which core is then covered with a skin. This skin is generally made of layers of reinforcements (such as fiber fabrics) embedded in a resin. A relatively light and rigid composite structure is thus obtained. Of course, boards of very different characteristics will be obtained depending on the nature of the materials constituting the skins, which can range from a single sheet of thermoformed ABS resin to a composite sandwich complex through the glass fiber composites. / carbon / Kevlar embedded in polyester or epoxy resins.

  With such a method of manufacture, the core therefore requires long and complex shaping operations, because it is often a question of producing a final three-dimensional shape essentially comprising curved surfaces. Often, this manufacture requires a long manual operation of finishing the core by planing and sanding.

  It has already been proposed that these cores be directly molded to the desired shape, either by injection into a mold, or by expansion in the mold. In this case, the final core is obtained in a simpler and often faster way. However, the speed of the molding operation is relative insofar as it is necessary to allow time for the foam to be distributed inside the mold and to crosslink. Such a cycle generally requires at least about ten minutes. During this time, the mold is made unavailable, so that, if one wants to make a large number of cores, it will invest in many identical molds, which also requires a large area for the unit of production.

  Moreover, in the two manufacturing processes just described, there is a tendency to obtain a core in which the foam has a substantially uniform density throughout the core. This is not necessarily an optimal solution.

  Indeed, a gliding board sees its characteristics and performance determined according to its external geometry on the one hand, and according to its various flexural and torsional stiffness characteristics. But with a traditional construction, these two elements are not independent. Indeed, the ends of the boards are generally thin, and it is difficult to obtain that these ends are as rigid and solid as it would be desirable. Moreover, it is known that certain parts of the board, such as those located under the feet of the user will be mechanically more stressed than others. However, with a homogeneous density core, there is a risk of having to choose a dense material depending on the stresses in the most stressed areas, while one could be content with less dense materials, in other areas. We are therefore led to increase the weight of the board.

  Of course, in order to avoid this, reinforcements located in the most stressed areas are generally provided. But the implementation of these reinforcements requires additional operations, and the supply of additional material.

  The object of the invention is therefore to propose a new method for manufacturing a board that makes it possible to produce nuclei with variable densities in a simple and economical manner.

  For this purpose, the invention provides a method for manufacturing a gliding board, characterized in that it comprises the distinct steps of: manufacturing a foam core blank; - Proceed to a step of shaping the core by thermoforming with compression of material of the foam blank; cover the core with an outer skin.

  The invention also relates to a gliding board comprising at least one foam core covered with an outer skin, characterized in that the foam core has zones of different densities without discontinuity of material, said board being obtained for example by a process comprising, for producing the core, a thermoforming step with compression of material.

  Other features and advantages of the invention will appear on reading the detailed description which follows and in view of the appended drawings in which: FIGS. 1, 2 and 3 are diagrammatic views respectively from above, from side and from end of a kitesurf board; Figure 4 is a side view of a rectangular foam bar; Figure 5 is a side view of the foam roll of Figure 4 after undergoing a first roughing operation consisting of material removal in the thickness direction.

  - Figures 6, 7 and 8 are diagrammatic views respectively side, top, and end of the core of a kitesurf board after undergoing a shaping step by thermoforming with compression of material; Figure 9 is an enlarged, partial sectional view of the kitesurf board obtained by the method of the invention.

  Figures 10 and 11 are top and side views of a second embodiment of a blank core for a board according to the invention; Figure 12 is a sectional view of the core obtained according to the method of the invention from the foam blank shown in Figures 9 and 10.

  FIGS. 1 to 3 illustrate an example of a kitesurf board 10, whose external shapes correspond substantially to what can be found on the market. The board is essentially flat and thin. However, it has, as can be seen in the side view of Figure 2 a significant longitudinal curvature. The lateral edges 12 of the board are arched and the board also has transverse end edges 14 arcuate. Preferably, the board is slightly thicker in its center than near its edges 12, 14. The lower face 16 of the board, which forms the hull, has for example a slight concave which extends longitudinally in its center , the longitudinal edges of the hull are however substantially planar.

  Of course, the board is equipped with accessories such as, on its upper face, fasteners to tighten the feet of the user, and on its underside, four fins 18 arranged near the four corners of the board. On the upper face 20, also called bridge, the board has fasteners 22 in which the user can slide his feet to drive the board.

  Of course, this example of a gliding board is not limiting, and it could have another geometry or be equipped with other accessories, etc ...

  In accordance with the teachings of the invention, and as shown in FIG. 9, the board comprises a foam core 24 which is covered with an outer skin 26 and which has zones of different densities without discontinuity of material.

  The principle of the invention is based on the production, from a blank 23, of a foam core 24 which preferably has a shape close to that of the final board, this shape being acquired before the core 24 is covered with the outer skin 26, and this shape is obtained by a method comprising at least one thermoforming step with compression of material.

  Thus, it will be possible, for example, to start from an initial parallelepipedal foam roll 21 as illustrated in FIG. 4. This bread then has an initial length L0, a width 10 and a height HO. In most cases, however, depending on the mode of production of this initial bread, it will have a relatively homogeneous density. Optionally, for example if the bread 21 is directly obtained by molding, it may have a surface crust of higher density, but this crust will be substantially homogeneous over the entire surface of the bread. Preferably, use will be made of a thermoformable foam, for example a PVC foam such as those sold under the trademark AIREX. Other materials are usable, including extruded polystyrene foams, and more generally all synthetic resin-based foam materials.

  From this raw form 21, it will be sought to obtain a rough shape 23 of the core. This step is not mandatory, especially if the initial loaf 21 has already been obtained, for example by molding, with a suitable shape. However, in the illustrated case, there is provided a simple operation of shaping the bread 21 in the direction of its thickness. This leads to the blank 23 of the core shown schematically in Figure 5 on which it can be seen for example that the blank has a reduced thickness H1 at its longitudinal ends. This machining operation remains particularly fast and simple because, over a given width, the thickness of the blank is constant. This machining operation can be carried out in various ways, and in particular by cutting with hot wire or by planing.

  This blank 23 may possibly undergo other shaping operations before the thermoforming step with compression of material.

  This thermoforming step according to the invention consists in introducing the core blank 23 into the mold of a press (not shown), preferably a heating press. Preferably, the core blank 23 will have been heated beforehand and brought to a temperature close to the thermoforming temperature of the foam. The mold will have rigid face preferences.

  Once in the mold, the blank is subjected to a compressive force which causes, at least in certain areas, deformation of the foam by crushing, and because this pressure is applied under a temperature at least close to the temperature thermoforming, this deformation becomes permanent. Thus, after the cooling and opening of the mold, the foam will have definitively taken the shape of the core 24.

  In the exemplary embodiment illustrated in FIGS. 6, 7 and 8, it can be seen that the initial foam roll 21 had longitudinal and transverse dimensions which were much greater than those of the core 24 so that, after the thermoforming operation, it it is necessary to carry out a kernel cutting operation 24 along its contour line C. Alternatively, it can be provided that the mold of the press is provided with cutting edges along this contour line, the cutting operation is then performing simultaneously with that of thermoforming. It is also possible that the blank 23 has a contour sufficiently close to that of the core so that no cutting is necessary.

  In the example illustrated, the core has been produced in a mobile press only in one direction, namely in the direction of the thickness of the blank 23 and the core 24. However, it is possible to envisage using a mold whose lateral flanks, corresponding for example to the longitudinal edges of the blank, would also be movable in a transverse direction, so as to subject the blank compression in two directions.

  By using a PVC foam having an initial density of 80 kg / m 3, this thermoforming operation can be carried out at a temperature of 80 C under a pressure of 8 bar and with a duration of 220 seconds.

  In some cases, especially when certain areas are intended to undergo a high densification ratio, it may be provided that the thermoforming step with compression of material is conducted in several progressive sub-steps, these different substeps using, for example different molds.

  As will be understood, the different zones of the foam core will thus each have undergone a force and a compression amplitude which essentially depends on the initial thickness of the blank in this zone and the final thickness imposed by the corresponding faces of the mold in closed position. However, the tests showed that, under the above conditions, it was possible to locally reduce the thickness of the foam to less than a quarter of its initial thickness, that is to say by multiplying its density by at least a factor of 4, without the foam being damaged. On the contrary, the foam thus densified is more resistant, both in flexion and in compression. Such benefits will be clearly perceptible once a densification rate of about 20% has been reached, and will be obvious with a densification rate of 100%, corresponding to a doubling of the initial density of the foam.

  As illustrated in FIG. 9, it is thus possible to obtain, at the edges 12, 14 of the board 10, a local reinforcement of the material of the core, which will result in a greater resistance of the edges of the boards, which are particularly exposed to shocks.

  In the illustrated example, in which the core blank has undergone a preliminary machining step to reduce the thickness of its ends to the thickness H1 less than HO, the densification ratio of the core at the longitudinal ends the board will therefore be smaller than the densification ratio observed near the longitudinal edges. We can easily play on different flexibilities in different areas of the board. However, the entire peripheral zone of the core has a density greater than that of a central zone.

  However, it should be noted that the thermoforming step according to the invention may well leave some areas of the core blank perfectly intact, without any deformation. Similarly, it may also impose, in certain areas, geometric deformations that do not involve significant compression of the material. Some areas may be bent only by thermoforming, which for thin parts, involves virtually no compression of the material.

  As illustrated in FIGS. 10 to 12, the invention will also be particularly useful for locally reinforcing other zones of the board than the peripheral zone, in particular the zones that are intended to receive accessories such as the fasteners 22 or the 3 0 ailerons 18.

  Thus, it can be expected that the core blank has extra thicknesses (in the compression direction provided for the shaping step) corresponding to the core areas in which it wants to densify the foam. In the illustrated example, it is chosen to densify the zones of the boards intended to receive the fasteners 20. In fact, these core areas of planks must firstly allow a solid anchoring of the fasteners, and secondly they must directly withstand the pressure forces due to the support of the user. It is therefore particularly interesting to strengthen them. Thanks to the invention, this is achieved in a particularly simple manner. As can be seen, extra thicknesses 28 are provided in the blank, in the areas to be densified. These overthicknesses are obtained directly by molding, if the initial foam roll is obtained in this way, or they are obtained by machining, by hand (planing, sanding, etc.) or by machine (numerically controlled milling machine, etc. ..).

  After the thermoforming step with compression of material according to the invention, the core illustrated in FIG. 12 is effectively reinforced in the predefined zones. This local reinforcement will allow the introduction of inserts in the core, which allow the anchoring of fixings.

  The same technique of local densification of the core may for example be used to create in the core stiffening beams, directly integrated into the core, without discontinuity of material. For example, if one wants to increase the stiffness of the board in torsion, one can predict that the core has beams diagonally, each joining two opposite corners of the board. We can also create in the core a central longitudinal beam, well known in the field of the manufacture of surfboards.

  The invention can also be applied to snowboards, skis in general (alpine skis, cross-country skis, cross-country skis, ...), water skis and wakeboard boards.

  Finally, the technique of thermoforming with compression of material may also be used to create simple decorative patterns hollow and / or raised, for example on the upper face of the board.

  Thanks to the invention, it is therefore possible to densify and reinforce the nucleus locally, exactly where it is necessary. Unlike some cores of the prior art in which local reinforcements are integrated in the form of inserts material different from the core material of the core, the technology according to the invention allows to maintain a continuity of the material of the core between the low density areas and denser areas. In addition, it is very easy to create a gradual density gradient, to avoid having a sudden discontinuity of density between low density and dense areas. For this, it is sufficient that the height variation on the edge of the allowance provided on the blank is progressive (as is illustrated in Figure 11 for the extra thickness 28). This avoids areas of sudden change in mechanical characteristics of the core, areas that are always the place of concentration stress under stress and therefore always weakened.

  Of course, the formatting of the core by thermoforming makes it possible to obtain at the same time the external geometrical shapes that one wants to give to the board, in particular its thickness profile, any hull shapes, and / or readings. front or back shaped spatula. However, it is also possible that the shape of the core 24 is corrected after the thermoforming step by a complementary operation, for example by shaping by machining, so by removal of material.

  The initial density of the core foam will of course be chosen according to the desired final characteristics for the gliding board, in particular the desired stiffness and solidity. Of course, account will also be taken of the weight / volume ratio for the board, especially if specific buoyancy characteristics are desired. In this context, the possibility of densifying the foam selectively will maintain a low foam density in the less stressed areas.

  In the illustrated examples, the gliding board has only one core. However, for various reasons, it can be envisaged to use several nuclei, for example two superposed nuclei. Within the finished board, these two cores can be separated for example by a reinforcing layer such as a sheet of fiber fabrics impregnated with resin, a metal strip, etc. In all cases, it will then be possible to provide only one of the cores will be shaped according to the technique of the invention.

  Of course, once the core made in accordance with the teachings of the invention, the manufacture of the board can be continued according to the usual techniques. All the usual materials can be used to make the skin intended to cover the core. This skin to contain for example a single sheet of thermoformed ABS resin, a composite sandwich complex, fiberglass / carbonelkevlar composites embedded in polyester or epoxy resins. The skin may also include localized reinforcements such as very high density foams, alveolar honeycomb type materials, etc.

  As illustrated in FIG. 9, the board may also be provided along its edges with a plastic peripheral reinforcement 30, for example made of ABS.

  For the realization of a kitesurf board it was found that it could be interesting to use in the skin of the board a metal reinforcement. This metal reinforcement is for example made in the form of an aluminum alloy sheet a few tenths of millimeters thick. This metal sheet, covering for example the upper surface of the board, is embedded in a resin (preferably thermosetting). To reduce the weight, it may be provided that it comprises recesses, for example holes 25 regularly distributed over its entire surface.

  The use of these various materials intended to form the outer skin may require subjecting the assembly to significant temperatures and pressures. Tests have shown that a nucleus' made according to the invention could withstand without difficulty a step of manufacturing the skin requiring temperatures of the order of 120 C for periods of the order of 10 minutes. These conditions therefore allow the use of all the usual materials.

Claims (1)

8 claims   1. A method of manufacturing a gliding board (10), characterized in that it comprises the separate steps of: manufacturing a blank (23) of core (24) foam; performing a step of shaping the core (24) by thermoforming with material compression of the foam blank (23); covering the core (24) with an outer skin (26).   2. Processes according to claim 1, characterized in that the foam of the core (24) is a rigid foam.   3. Method according to one of claims 1 or 2, characterized in that the core foam (24) is a thermoplastic foam.   4. Method according to any one of the preceding claims, characterized in that the forming step by thermoforming with compression of material of the nucleus induces in the core (24) zones of different densities.   5. Method according to claim 4, characterized in that the step of shaping by thermoforming with compression of the core material induces in the core areas whose density differs by at least 20% of the initial density of the foam .   6. Method according to one of claims 4 or 5, characterized in that the shaping step by thermoforming with material compression induces in the core (24) a peripheral zone of higher density.   7. Method according to any one of claims 4 to 6, characterized in that the step of forming by thermoforming with compression of material induces in the nucleus an area of higher density in an area corresponding to a surface area. support for a user's feet.   8. A method according to any one of the preceding claims, characterized in that the forming step by thermoforming with compression of material preserves areas in which the foam does not undergo compression.   9. Gliding board comprising at least one foam core (24) covered with an outer skin (26), characterized in that the foam core (24) has zones of different densities without discontinuity of material between said zones .   Sliding board, characterized in that the core is obtained by a process comprising a material compression thermoforming step according to any one of claims 1 to 8.